CN113070445B - Large-caliber nodular cast iron pipe die coating and preparation method and application thereof - Google Patents
Large-caliber nodular cast iron pipe die coating and preparation method and application thereof Download PDFInfo
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- CN113070445B CN113070445B CN202110322048.4A CN202110322048A CN113070445B CN 113070445 B CN113070445 B CN 113070445B CN 202110322048 A CN202110322048 A CN 202110322048A CN 113070445 B CN113070445 B CN 113070445B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
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- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D13/00—Centrifugal casting; Casting by using centrifugal force
- B22D13/02—Centrifugal casting; Casting by using centrifugal force of elongated solid or hollow bodies, e.g. pipes, in moulds rotating around their longitudinal axis
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Abstract
The water-based centrifugal casting pipe die coating for the large-caliber nodular cast iron is prepared by selecting perlite and diatomite with different particle sizes as mixed refractory aggregates, matching with a composite suspending agent consisting of sodium bentonite and/or lithium bentonite and carboxylated rectorite, adding hollow microspheres and a common binder, and has excellent suspension stability, high-temperature crack resistance, low gas evolution property, permeability and hygroscopicity. Meanwhile, the invention also adjusts and optimizes the specific spraying process, coats the large-caliber nodular cast iron pipe die coating on the surface of the pipe die, and prepares the large-caliber nodular cast iron pipe after centrifugal casting, wherein the surface of the large-caliber nodular cast iron pipe has no surface defects such as air holes, bonded sand, shrinkage cavities and the like, and the surface quality is excellent.
Description
Technical Field
The invention belongs to the technical field of refractory coatings, and particularly relates to a large-caliber nodular cast iron pipe die coating as well as a preparation method and application thereof.
Background
Centrifugal casting is a casting method for pouring and forming under a centrifugal force field, and is a main method for producing large-caliber nodular cast iron pipe fittings. The pipe die is a hot-state working die in centrifugal casting, bears sharp heat exchange load in continuous production, and can generate hot crack grids after the accumulation of residual stress exceeds the ultimate strength of a material, and the pipe die can be scrapped to a certain extent. The pipe die is expensive, and in order to reduce the production cost, improve the pipe die production condition, and prolong the pipe die life, the effective methods for protecting the pipe die at present have two kinds: and coating casting paint and resin sand. The cast pipe produced by the resin sand method has poor surface quality, and harmful gas produced in the production pollutes the environment and is eliminated by the coating method.
The casting coating is a layer of casting auxiliary material which is used for being attached to a casting mould and a core in the casting process to play a role in isolating molten metal and has a specific function. The casting paint is composed of refractory filler, liquid carrier, adhesive, suspension stabilizer and other assistants. Casting coatings generally have the following specific functions: preventing the casting from sand burning; the surface smoothness of the casting is improved; reinforcing the surface of the sand core; shielding or isolation (S, N and other gases); prevent casting defects (veins, sintering pores, sand pores, etc.); alloying the surface of the casting and refining grains; adjusting the solidification temperature field (enthalpy change casting coating and heat preservation casting coating) of the casting; the sand falling and cleaning labor amount of the casting is reduced, and the working hours are saved. Because the high-temperature molten iron directly acts on the surface of the coating, the surface temperature of the coating reaches 1200-1300 ℃ at the moment of pouring, the performance of the coating needs to be kept stable in the state, and the phenomena of melting, decomposition, softening and the like cannot occur.
However, in the prior art, due to the unreasonable formula of the casting coating and the imperfect parameter setting of the casting process, the castings produced by the centrifugal casting process are easy to have surface defects such as sand sticking, air holes, cracks, lapping, shrinkage cavities, strip-shaped lamination, rain or the like. In view of the above, it is desirable for the skilled practitioner to overcome various defects occurring in the centrifugal casting process from the aspects of the formulation composition of the casting coating, the parameter setting of the casting process, and the like. For example: patent literature invented by shozui et al (CN2013103687637, high-alloy tube centrifugal casting high-temperature coating and manufacturing method thereof) discloses adding quartz powder and zircon powder to improve high-temperature resistance, adjust casting system thermal resistance, and control cooling speed of casting tube; the water glass and the silica sol are high-temperature binders, so that the adhesion effect of the coating under a high-temperature condition can be improved, bubbles are prevented from appearing on the surface of the coating, the initial bonding strength of the coating can be increased by adopting polyvinylpyrrolidone, hydroxypropyl methylcellulose and seaweed gel, the phenomena of air holes, slag inclusion, burrs and the like are avoided, and the quality of the high-alloy centrifugal casting pipe is improved.
The patent document (CN201210042129x, preparation and construction method of pipe die coating) invented by Kongshun et al discloses a pipe die coating composed of bentonite, diatomite, powdered perlite and water, and by optimizing the preparation process of the coating, the coating with lower gas evolution, higher strength, higher suspension property and better mold release property is successfully obtained, the forming qualification rate of the pipe is improved, and the appearance quality of the pipe is improved.
Therefore, from the aspects of formula composition of casting coatings, parameter control of casting process and the like, solving various defects in the centrifugal casting process is still the research focus, hot spot and difficulty of the industry. As is known, diatomite is a commonly used waterproof powder material in casting coatings, mainly consists of skeleton remains fossil of unicellular aquatic algae plants, has the characteristics of high porosity, strong adsorbability, small volume weight, high melting point, heat insulation, sound absorption, low refractive index, stable chemical performance and the like, belongs to non-renewable resources, and has higher cost.
Therefore, how to prepare the pipe die coating which has low cost, excellent performance and high surface quality and is suitable for the large-caliber ball-milling cast iron has important practical significance and market application prospect.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide the large-caliber nodular cast iron pipe die coating which is simple in proportioning and low in cost, and has high erosion resistance, high fire resistance, high demolding performance, low gas evolution, permeability and hygroscopicity and long-term storage stability.
The invention also aims to provide a preparation method of the large-caliber nodular cast iron pipe die coating.
The invention also aims to provide the application of the large-caliber nodular cast iron pipe die coating, a refractory coating is prepared by a specific spraying process, and the large-caliber nodular cast iron pipe prepared by a centrifugal casting process has good surface quality.
In order to achieve the purpose, the invention adopts the following technical scheme that the large-caliber nodular cast iron pipe die coating comprises the following raw materials in parts by weight:
100-150 parts of perlite, 0-30 parts of diatomite, 3-10 parts of composite suspending agent, 0-15 parts of binder, 0.05-0.5 part of hollow microsphere and 300 parts of water.
The perlite comprises, in weight percent, 25-40% of first particles having a particle size of 50< d <60 μm, 50-70% of second particles having a particle size of 37< d <48 μm, and 5-10% of third particles having a particle size of d <30 μm; the content of silicon dioxide is 80-85%;
the diatomaceous earth comprises, in weight percent, greater than 90% of a particle size having a particle size of 25< d <38 μm, a silica content greater than 85%;
the composite suspending agent comprises 60-80% of sodium bentonite and/or lithium bentonite and 20-40% of carboxylated rectorite in percentage by weight.
The binder is selected from one or more of water glass, aluminum phosphate, sodium tripolyphosphate, polyvinyl alcohol, polyvinyl acetate or polyacrylate.
The hollow microsphere has an average particle diameter of 40-70 μm, occupies a cavity of 70% or more of the total volume of the hollow microsphere, has a softening point of 1200-1450 ℃, a Mohs hardness of 5-6, and a compressive strength of 20-40MPa, and is prepared from silicate or metal oxide.
Preferably, the large-caliber nodular cast iron pipe die coating comprises the following raw materials in parts by weight: 120-150 parts of perlite, 10-20 parts of diatomite, 5-10 parts of composite suspending agent, 5-15 parts of binder, 0.25-0.5 part of hollow microsphere and 300 parts of water.
Preferably, the large-caliber nodular cast iron pipe die coating comprises the following raw materials in parts by weight: 120-150 parts of perlite, 5-15 parts of diatomite, 5-8 parts of composite suspending agent, 5-12 parts of binder, 0.25-0.4 part of hollow microsphere and 250 parts of water.
Preferably, the large-caliber nodular cast iron pipe die coating further comprises the following auxiliary agents, such as a dispersing agent, a leveling agent, an antifoaming agent, a mineralizing agent, a suspension stabilizer and the like, and the addition amount of the auxiliary agents is 1-3% of the total weight of the coating.
The viscosity of the large-caliber nodular cast iron pipe die coating is 40-45s (T6 cup viscosity).
The invention also provides a preparation method of the large-caliber nodular cast iron pipe die coating, which comprises the following steps:
(1) preparation of composite suspending agent
1. Weighing 100 parts of rectorite by weight, adding the rectorite into 1000 parts of water, uniformly stirring, heating to 70-80 ℃, adding 5-10 parts of silane compound containing amino, reacting for 12-14h, and filtering to obtain amino modified rectorite;
2. and (2) mixing the amino modified rectorite and succinic anhydride obtained in the step (1) according to the ratio of carboxyl to amino 1: 1, adding the mixture into a solvent, adjusting the pH value to 4.0, reacting for 6-7h, filtering and drying to obtain the carboxylated rectorite;
3. uniformly mixing the carboxylated rectorite obtained in the step (2) with sodium bentonite and/or lithium bentonite according to the formula ratio to prepare the composite suspending agent;
(2) weighing 1/2 parts of water, mixing with the composite suspending agent obtained in the step (1), stirring for 6-10h, adding the binder and the diatomite, stirring for 1-2h, adding the rest water, the perlite and the hollow microspheres, and stirring for 2-4 h;
(3) and (3) transferring the mixture prepared in the step (2) into a colloid mill, grinding for 1-2h, transferring into a launching tank, standing at room temperature for 12h, and aging to obtain the large-caliber nodular cast iron pipe die coating.
The invention also provides a construction method of the large-caliber nodular cast iron pipe die coating, which comprises the following steps:
(1) cleaning the pipe die, heating to 160-200 ℃ and keeping the axial temperature difference less than or equal to 30 ℃ for later use;
(2) and (2) spraying the large-caliber nodular cast iron pipe die coating to the pipe die in the step (1), wherein the distance between a nozzle and the pipe die is 200-400mm, the rotating speed of the pipe die is 40-60r/min, the spraying wind pressure is 0.4-0.6MPa, the pressure of a spraying pipeline is 0.25-0.4MPa, the pot pressure of a spraying tank is 0.45-0.55MPa, and the thickness of the spraying coating is 0.8-1.2 mm.
The invention also provides application of the large-caliber nodular cast iron pipe die coating for preparing large-caliber nodular cast iron pipes, such as DN1100-DN2600, wherein the prepared iron pipes have the tensile strength of more than or equal to 430Mpa, the minimum elongation of more than or equal to 9 percent, the spheroidization grade of 1-3, the graphite size grade of more than or equal to 6 grade, the content of cementite of less than or equal to 1 percent and the metallographic structure of pearlite of less than or equal to 25 percent.
Compared with the prior art, the invention has the following beneficial effects:
(1) in order to prepare the pipe die coating which is low in cost, excellent in performance and high in surface quality and is suitable for large-caliber nodular cast iron, the water-based centrifugal casting pipe die coating is prepared by taking perlite and diatomite as mixed refractory aggregate, matching with a composite suspending agent consisting of sodium bentonite and/or lithium bentonite and carboxylated rectorite, and hollow microspheres and adding a common binder.
Compared with diatomite, the perlite has low water absorption and gas generation, high heat resistance and lower cost, and the pipe die coating with excellent performance and higher surface quality can be prepared by selecting the perlite as the main component of the refractory aggregate and matching a small amount of diatomite with small particle size;
on the other hand, sodium bentonite and/or lithium bentonite are commonly used suspending agents, and are commonly used together with suspending stabilizers such as sodium carboxymethylcellulose and sodium alginate, however, the foaming properties of the sodium carboxymethylcellulose and the sodium alginate are high, and the defects such as air holes and the like on the surface of a casting are easily caused;
on the other hand, the hollow microspheres with specific structures are added, so that the air permeability, the heat insulation property and the high-temperature crack resistance of the coating are improved, and the defects of pores, sand adhesion, cracks and the like on the surface of the heavy-caliber nodular cast iron casting are avoided.
(2) In order to ensure that the spraying effect of the coating is good and the coating on the surface of the die is uniform and smooth in the whole production process, the coating is required to be free from precipitation and delamination within a long time and to be kept in a suspension state for a long time. Therefore, the perlite and the diatomite with different particle size ratios are selected for compounding, so that aggregate particles with different particle sizes are well embedded, gaps among the aggregates are reduced, the number of effective binding liquid is increased, the suspension effect is improved, the permeability of the coating is reduced, the drying speed is high, and the moisture absorption of the coating is reduced; further, the composite suspending agent with a specific structure and combination is selected to further ensure that the pipe die coating has good suspensibility.
(3) According to the invention, the large-caliber nodular cast iron pipe die coating is coated on the surface of the pipe die through a specific spraying process, the coating has low air permeability and high-temperature crack resistance, and the large-caliber nodular cast iron pipe prepared by centrifugal casting has excellent surface quality.
(4) According to the invention, perlite with lower cost is selected as the main refractory aggregate, so that the dosage of diatomite is greatly reduced, the cost is saved, and the sustainable development of the green environment is facilitated.
Drawings
FIG. 1 shows the effect of the heavy-calibre nodular cast iron pipe die coating of the invention after spraying.
Fig. 2 shows the effect of the heavy caliber nodular cast iron pipe of the invention after casting.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The specific embodiment is as follows:
1. preparation of large-caliber nodular cast iron pipe die coating
The invention provides a preparation method of a large-caliber nodular cast iron pipe die coating, which comprises the following steps:
(1) preparation of composite suspending agent
1. Weighing 100 parts by weight of rectorite, adding the rectorite into 1000 parts by weight of water, uniformly stirring, heating to 80 ℃, adding 6 parts by weight of silane compound (KH550) containing amino, reacting for 12 hours, and filtering to obtain amino modified rectorite;
2. and (2) mixing the amino modified rectorite and succinic anhydride obtained in the step (1) according to the ratio of carboxyl to amino 1: 1, adding the mixture into a solvent, adjusting the pH value to 4.0, reacting for 6 hours, filtering and drying to obtain carboxylated rectorite;
3. uniformly mixing the carboxylated rectorite obtained in the step 2 with sodium bentonite and/or lithium bentonite according to the formula amount in the table 1 to prepare the composite suspending agent;
(2) weighing water with the formula amount of 1/2, mixing the water with the composite suspending agent obtained in the step (1), stirring for 10 hours, adding the binder and the diatomite, continuously stirring for 1 hour, adding the rest water, the perlite and the hollow microspheres, and continuously stirring for 4 hours;
(3) and (3) transferring the mixture prepared in the step (2) into a colloid mill, grinding for 2h, transferring into a launching tank, standing at room temperature for 12h, and aging to obtain the large-caliber nodular cast iron pipe die coating.
TABLE 1
Wherein the perlite A comprises, in weight percent, 40% of first particles having a particle size of 50< d <60 μm, 50% of second particles having a particle size of 37< d <48 μm, and 10% of third particles having a particle size of d <30 μm;
the perlite B comprises, in weight percent, 25% of first particles having a particle size of 50< d <60 μm, 70% of second particles having a particle size of 37< d <48 μm, and 5% of third particles having a particle size of d <30 μm;
the perlite C comprises, in weight percent, 30% of first particles having a particle size of 50< d <60 μm, 60% of second particles having a particle size of 37< d <48 μm, and 10% of third particles having a particle size of d <30 μm.
2. And (3) performance testing:
2.1 suspension test
The suspension property measurement method adopts a standing method, the prepared coating is placed in a 100ml measuring cylinder, and after the coating is kept stand for 24 hours, the percentage of the volume of the clear liquid to the volume of the whole coating suspension is observed.
2.2 air Forming test
The gas forming amount of the coating is the volume of gas volatilized by the coating at high temperature in unit mass fraction, the unit is ml/g, an intelligent gas forming tester is adopted for testing, the testing temperature is 1200 ℃, and the testing time is 2 min.
2.3 Permeability test
The depth of penetration of the coating is usually examined by immersing a standard molding sand sample in the coating for 3 seconds and drying, sawing the sample, and measuring the depth of penetration of the coating on the cross section of the sample with a caliper.
2.4 high temperature crack resistance test
Placing the sand sample which is uniformly coated with the coating and dried in a box type furnace at 1200 ℃ for carrying out quick heating and heat preservation for 2min, quickly opening a furnace door to observe whether cracks exist and the condition that the size and the number of the cracks are relative to the cracks of the coating can be evaluated according to the following 4 grades:
stage I: the surface is smooth and has no cracks, or has only extremely fine cracks, and the phenomenon of peeling between the substrate and the coating is avoided;
II stage: fine net-shaped or dendritic cracks are formed on the coating, the width of each crack is less than 0.5mm, and the phenomenon of stripping between the matrix and the coating is avoided;
grade III: the coating has reticular or dendritic cracks, the width is less than 1mm, the cracks are deep, no through coarse cracks exist, and the stripping phenomenon does not exist between the matrix and the coating;
stage IV: the coating has reticular or dendritic cracks with a width larger than 1mm, through cracks and peeling between the substrate and the coating.
2.5 viscosity test, paint viscosity was measured using T6 cups.
2.6 moisture absorption test
The casting paint coating sample with the mass of M0 after weighing is placed in a constant humidity box to keep the temperature at 23 +/-1 ℃ and the relative humidity at 95 +/-1 percent, and after the sample is placed for 24 hours, the mass of the test sample is M1, and the moisture absorption rate of the casting paint coating is (M1-M0)/M0 multiplied by 100 percent.
Wherein the test results of the large-caliber nodular cast iron pipe die coating of the embodiments 1 to 6 are shown in the table 2:
TABLE 2
| Testing | Example 1 | Example 2 | Example 3 | Example 4 | Example 5 | Example 6 |
| Viscosity (T6, s) | 40.6 | 41.8 | 44.6 | 42.3 | 43.1 | 42.9 |
| Suspension (%) | 95 | 96 | 97 | 97 | 96 | 95 |
| Gas evolution (ml/g) | 2.92 | 3.41 | 4.06 | 3.56 | 4.13 | 3.85 |
| Permeability (mm) | 2.3 | 4.5 | 3.8 | 3.4 | 4.1 | 3.7 |
| High temperature crack resistance | Class I | Class I | Class I | Class I | Class I | Class I |
| Moisture absorption Rate (%) | 0.9 | 1.2 | 1.5 | 1.8 | 1.6 | 1.2 |
From the experimental data in table 2, it can be found that the large-caliber nodular cast iron pipe die coating prepared by the invention has good moderate viscosity, high suspension property, low permeability and good construction performance, and the coating has low hygroscopicity after being dried, so that the operable time of a centrifugal casting process is prolonged, and the excellent surface quality of the prepared iron pipe can be ensured due to the low gas evolution and excellent high-temperature crack resistance of the coating.
3. Comparative examples
The invention provides the following comparative examples, which are compared with the large-caliber nodular cast iron pipe die coating described in example 6.
Comparative example 1
Without perlite, the perlite was replaced with an equal amount of diatomaceous earth, the remaining composition and proportions being exactly as in example 6.
Comparative example 2
The carboxylated rectorite was not contained, and the same amount of sodium bentonite was used in place of the carboxylated rectorite, and the composition and the proportion were completely the same as in example 6.
Comparative example 3
The carboxylated rectorite was not contained, and the same amount of sodium carboxymethylcellulose was used in place of the carboxylated rectorite, and the composition and the ratio were completely the same as in example 6.
Comparative example 4
The composition and the proportion of the composition are completely the same as those in example 6.
Comparative example 5
The carboxylated rectorite was not contained, and the same amount of rectorite was used instead of the carboxylated rectorite, and the composition and the proportion were completely the same as in example 6.
Comparative example 6
The composition of perlite C comprises, in weight percent, 90% of a second particle having a particle size of 37< d <48 μm and 10% of a third particle having a particle size of d <30 μm, the remaining composition and proportions being exactly as in example 6.
Comparative example 7
The composition of perlite C comprises, in weight percent, 90% of first particles having a particle size of 50< d <60 μm and 10% of third particles having a particle size of d <30 μm, the remaining composition and proportions being exactly as in example 6.
Comparative example 8
The composition and proportions were identical to those of example 6, except that no diatomaceous earth was included.
Wherein the test results of the large-caliber nodular cast iron pipe die coating of the comparative examples 1 to 8 are shown in Table 3:
TABLE 3
From the experimental data in table 3, it can be seen that the invention adopts the perlite and diatomite with specific particle size combination as the refractory aggregate, and selects the carboxylated rectorite as the component of the composite suspending agent, which can improve the properties of the large-caliber nodular cast iron pipe die coating, such as suspension property, high-temperature crack resistance and the like, and simultaneously reduce gas evolution, permeability and hygroscopicity, and can be suitable for preparing the large-caliber nodular cast iron pipe with excellent surface quality.
From the aspect of hygroscopicity, compared with sodium bentonite, sodium carboxymethylcellulose and unmodified rectorite, the carboxylated rectorite has reduced hygroscopicity, so that the construction time of the pipe die coating is greatly prolonged, and a cast pipe die coated with the rectorite can be placed for a long time without reducing the surface quality of a casting.
4. Application example of large-caliber nodular cast iron pipe die coating
The invention also provides a construction method of the large-caliber nodular cast iron pipe die coating, which comprises the following steps:
(1) cleaning the pipe die, heating to 160-200 ℃ and keeping the axial temperature difference less than or equal to 30 ℃ for later use;
(2) and (2) spraying the large-caliber nodular cast iron pipe die coating to the pipe die in the step (1), wherein the distance between a nozzle and the pipe die is 200-400mm, the rotating speed of the pipe die is 40-60r/min, the spraying wind pressure is 0.4-0.6MPa, the pressure of a spraying pipeline is 0.25-0.4MPa, the pot pressure of a spraying tank is 0.45-0.55MPa, and the thickness of the spraying coating is 0.8-1.2 mm.
The large-caliber nodular cast iron pipe die coating of the embodiment 6 is sprayed according to the construction method, and the method comprises the following steps:
(1) cleaning a pipe die, heating to 200 ℃, and keeping the axial temperature difference less than or equal to 30 ℃ for later use;
(2) and (2) spraying the large-caliber nodular cast iron pipe die coating to the pipe die in the step (1), wherein the distance between a nozzle and the pipe die is 400mm, the rotating speed of the pipe die is 60r/min, the spraying wind pressure is 0.5Mpa, the pressure of a spraying pipeline is 0.25Mpa, the pot pressure of a spraying pot is 0.5Mpa, and the thickness of the spraying coating is 0.8-1.2mm, which is shown in figure 1 specifically.
The pipe die coating prepared by the construction method is used for preparing a large-caliber nodular cast iron pipe DN 2200, and the prepared iron pipe has the tensile strength of more than or equal to 430Mpa, the minimum elongation of more than or equal to 9 percent, the spheroidization grade of 3, the graphite size grade of more than or equal to 6 grade, the cementite content of less than or equal to 1 percent and the pearlite content of less than or equal to 25 percent, and the metallographic structure is shown in figure 2.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (9)
1. The large-caliber nodular cast iron pipe die coating is characterized in that: the composite material comprises the following raw materials in parts by weight:
100-150 parts of perlite, 0-30 parts of diatomite, 3-10 parts of composite suspending agent, 0-15 parts of binder, 0.05-0.5 part of hollow microsphere and 300 parts of water;
the composite suspending agent comprises 60-80% of sodium bentonite and/or lithium bentonite and 20-40% of carboxylated rectorite in percentage by weight;
the perlite comprises, in weight percent, 25-40% of first particles having a particle size of 50< d <60 μm, 50-70% of second particles having a particle size of 37< d <48 μm, and 5-10% of third particles having a particle size of d <30 μm.
2. The large-caliber nodular cast iron pipe die coating of claim 1, wherein: the diatomaceous earth comprises, in weight percent, greater than 90% particles having a particle size of 25< d <38 μm.
3. The large-caliber nodular cast iron pipe die coating according to any one of claims 1 to 2, wherein: the binder is selected from one or more of water glass, aluminum phosphate, sodium tripolyphosphate, polyvinyl alcohol, polyvinyl acetate or polyacrylate.
4. The large-caliber nodular cast iron pipe die coating according to any one of claims 1 to 2, wherein: the hollow microsphere has an average particle diameter of 40-70 μm, occupies a cavity of 70% or more of the total volume of the hollow microsphere, has a softening point of 1200-1450 ℃, a Mohs hardness of 5-6, and a compressive strength of 20-40MPa, and is prepared from silicate or metal oxide.
5. The large-caliber nodular cast iron pipe die coating according to any one of claims 1 to 4, wherein: 120-150 parts of perlite, 10-20 parts of diatomite, 5-10 parts of composite suspending agent, 5-15 parts of binder, 0.25-0.5 part of hollow microsphere and 300 parts of water.
6. The large-caliber nodular cast iron pipe die coating according to any one of claims 1 to 4, wherein: 120-150 parts of perlite, 5-15 parts of diatomite, 5-8 parts of composite suspending agent, 5-12 parts of binder, 0.25-0.4 part of hollow microsphere and 250 parts of water.
7. The preparation method of the large-caliber nodular cast iron pipe die coating of any one of claims 1 to 6, which is characterized by comprising the following steps: the method comprises the following steps:
(1) preparation of composite suspending agent
1. Weighing 100 parts of rectorite by weight, adding the rectorite into 1000 parts of water, uniformly stirring, heating to 70-80 ℃, adding 5-10 parts of silane compound containing amino, reacting for 12-14h, and filtering to obtain amino modified rectorite;
2. and (2) mixing the amino modified rectorite and succinic anhydride obtained in the step (1) according to the ratio of carboxyl to amino 1: 1, adding the mixture into a solvent, adjusting the pH value to 4.0, reacting for 6-7h, filtering and drying to obtain the carboxylated rectorite;
3. uniformly mixing the carboxylated rectorite obtained in the step (2) with sodium bentonite and/or lithium bentonite according to the formula ratio to prepare the composite suspending agent;
(2) weighing 1/2 parts of water, mixing with the composite suspending agent obtained in the step (1), stirring for 6-10h, adding the binder and the diatomite, stirring for 1-2h, adding the rest water, the perlite and the hollow microspheres, and stirring for 2-4 h;
(3) and (3) transferring the mixture prepared in the step (2) into a colloid mill, grinding for 1-2h, transferring into a launching tank, standing at room temperature for 12h, and aging to obtain the large-caliber nodular cast iron pipe die coating.
8. The construction method of the large-caliber nodular cast iron pipe die coating of any one of claims 1 to 6, which is characterized by comprising the following steps: the method comprises the following steps:
(1) cleaning the pipe die, heating to 160-200 ℃ and keeping the axial temperature difference less than or equal to 30 ℃ for later use;
(2) and (2) spraying the large-caliber nodular cast iron pipe die coating to the pipe die in the step (1), wherein the distance between a nozzle and the pipe die is 200-400mm, the rotating speed of the pipe die is 40-60r/min, the spraying wind pressure is 0.4-0.6MPa, the pressure of a spraying pipeline is 0.25-0.4MPa, the pot pressure of a spraying tank is 0.45-0.55MPa, and the thickness of the spraying coating is 0.8-1.2 mm.
9. The use of the large-caliber nodular cast iron pipe die coating of any one of claims 1 to 6 for preparing a large-caliber nodular cast iron pipe, wherein the prepared iron pipe has the tensile strength of more than or equal to 430MPa, the minimum elongation of more than or equal to 9 percent, and the metallographic structure with the spheroidization grade of 1 to 3, the graphite size grade of more than or equal to 6, the cementite content of less than or equal to 1 percent and the pearlite content of less than or equal to 25 percent.
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